Dispensing systems for dosing certain substances (e.g., chlorine) in fluids (e.g., recreational water bodies such as pools, spas, water parks, and the like) often require sensing the concentration of the substance. One type of sensor for such applications is an Oxidation-Reduction Potential (ORP) sensor for monitoring levels of chlorine in recreational water bodies. ORP sensors measure the ability of a substance to act as an oxidizing or reducing agent. Chlorine is an oxidizing agent, and the presence of chlorine in fluids can therefore be indirectly measured by the ORP sensor. ORP sensors are widely used due to their lower cost. However, ORP sensors may have several disadvantages. For instance, ORP sensors can have a non-linear signal response to chlorine concentration in the range of chlorine concentrations typically used in recreational water bodies (e.g., 1 to 10 ppm). Also, high impedance characteristics of ORP sensors may be sensitive to external electrical noise (e.g., stray electrical currents), thereby reducing the accuracy of measurement. Moreover, ORP sensors typically do not directly sense chlorine concentration and rather sense oxidation reduction potential, which in turn can be affected by various parameters such as pH, temperature, and the presence of other chemical species in the fluid. As a result, ORP sensors may need a calibration procedure to measure the ORP sensor response to chlorine concentration in a given water body. ORP sensors therefore must be “hand tuned” according to the physical conditions (e.g., pH, temperature, etc.) prevalent in each water body where ORP sensors are used. Such calibration procedures can become unreliable over time due to changing conditions in the water body and may increase equipment and maintenance costs.
Another type of sensor for measuring concentration of certain substances (e.g., chlorine) in a fluid (e.g., water) is an amperometric sensor. Such amperometric sensors can measure concentration of an ion based on an electric current (or changes therein) flowing between a pair of electrodes. Unlike ORP sensors, amperometric sensors can have a linear signal response to chlorine concentration and low electrical impedance. As a result, there may not be significant electrical noise interference in amperometric sensors resulting in better accuracy of measurement than ORP sensors. Such sensors also have a simple construction and low cost. In addition, amperometric sensors generally have predictable responses from sensor to sensor, eliminating the need for high cost calibration procedures.